The present invention generally relates to the field of damper operators, and more particularly, damper operators employing releasing devices such as bimetals or other heat responsive means which are used to actuate various fire protection equipment, such as their associated dampers, either in response to increases to heat in the vicinity of the device or in response to remote signals received thereby.
The present invention is particularly adapted for use with dampers comprising a frame having one or more rotating blades mounted therein. Conventionally, such dampers are provided with blade linkages which articulate the blades with respect to the frame so that the blades will move in unison between their open and closed positions with respect to the frame. It has long been known that such dampers may be operated using cables attached to the blade brackets or blade linkages of these dampers, which cables are normally threaded through a ferrule disposed through the damper/duct wall to reach an operator motor mounted outside of the duct in which the damper is located. It is also known to bias the blades towards the closed position, as for example, using springs extending between the damper frame and the blades, and to provide fusible links in the cable portion located within the duct so that, in response to increased temperatures within the duct, the cable will break and the spings cause the blades to move to the closed position, whereupon the passage of fire through the duct will be halted. Similar alternative arrangements have also been used for smoke dampers which are intended to move to the open position in response to the presence of smoke, and the herein below described invention is equally as applicable for use with such dampers.
Alternatively, it is known to operate dampers through a damper operator shaft, the rotation of which through an arc of 90.degree. corresponds to the rotation of the damper blades through 90.degree. between their open and closed positions. See, for example, the various damper operators disclosed in my prior issued U.S. Pat. No. 4,113,232, data Sept. 12, 1978 entitled, "Smoke, Fire And Air Control Damper With Stamped Blade."
For other damper, blade linkage, spring biasing, and operator constructions, please refer to the following U.S. Pat. Nos. 2,581,321; 2,654,921; 2,759,573; 2,996,768; 3,273,632; 3,327,764; 3,540,154; 3,727,663; 3,741,102; 3,814,165; 3,866,656; 3,899,156; 3,908,529; 1,368,453; 3,273,632; 3,908,529; 3,273,632; 3,543,439; and 3,908,529; British Specification No. 907, dated Jan. 13, 1904 and French Pat. No. 1,513,298.
Motorized operators for use in rotating damper operating shafts through an arc of 90.degree. are known. Such motorized operators normally may be controlled from a remote source to adjust air flow through the damper by rotating the damper blades a preselected number of degrees from the closed towards the open position, which degrees are normally assumed to correspond to the percentage of air flow through that damper. For example, a 10.degree. movement of the shaft normally corresponds to a 10.degree. opening of the damper which is assumed to establish a corresponding air flow approximately 11.degree. through the damper. In actuality, however, the relationship between arc of blade opening and air flow is not linear. In particular, during the initial stages of blade opening, correspondingly greater percentage volumes of air are permitted to pass through the damper for a given degree of blade opening, while as the damper blades approach their fully open positions correspondingly smaller increases in air flow are achieved per a given degree of blade rotation. No damper/operator unit is presently known having air flow characteristics which exhibit a substantially linear relationship between air flow and degree of operator shaft rotation.
While shaft/operated dampers may be preferred in certain instances, such operators are typically difficult and expensive to install, primarily due to the fact that such operators normally must be installed to the damper frame after that damper has been installed within the duct. Such a requirement makes installation difficult and expensive, often resulting in improperly installed damper-operator combinations.